Defensive Back - DB

What is Defensive Back - DB?

A defensive player who generally lines up slightly behind the
line of scrimmage, differing from defensive linemen and linebackers
who generally line up on the line of scrimmage. There are two main
specialized defensive back positions: the safety and the
cornerback.

Also known as the "secondary".

Sporting Charts explains Defensive Back - DB

Defensive backs will often line up against wide receivers to
protect against passing plays or move in on running plays and
prevent extended rushing gains. Defensive backs will also line up
against tight ends and running backs who are lined up away from
behind the quarterback.